Automatic valve systems or devices are known (U.S. Pat. No. 3.923.081) for preventing communication between waste pipes atmosphere and which operate so that the discharge of contaminated air is prevented but which to allow air to enter the pipes when a negative pressure occurs therein.
These valves satisfy requirements according to which the pipes projecting from roofs may be dispensed with and be replaced by pipes housed inside buildings on condition that the general pipeline is provided with an automatic valve which does not allow stale air to escape but which allows air to enter in the event of a negative pressure, e.g. on the flushing of water closets.